Curious as to what the base crit damage for all classes are and if they are the same?

Personally as a mage I've noticed my base crit damage APPEARS to be at 75%.
I suspect this because with 25% Crit damage from Determination my attacks seem to double exactly or within a couple k difference.
ie; Lightning hits 15k non crit, 29-31k with crit.

Also, has anyone come across some reliable formula for determining critical to rate ratio? or is this still unknown?